Between 17% and 22% of these patients had a primary or comorbid mental health diagnosis, and all the hospital stays added up to $3.5 billion in aggregate charges to the health care system. The most common diagnoses at the general hospitals were depression (44.1%), bipolar disorder (18.1%), and psychosis (12.1%). Substance abuse was a common comorbidity. In the freestanding hospitals, depression (42.2%), externalizing disorder (10.8%), and bipolar disorder (10.6%) were the most common psychiatric diagnoses.